This application claims the benefit of United Kingdom Patent Application No. GB0804029.7, filed on Mar. 4, 2008, which hereby is incorporated by reference in its entirety.
In the field of oil and gas exploration and production, various tools are used to provide a fluid seal between two components in a wellbore. Isolation tools have been designed for sealing an annulus between two downhole components to prevent undesirable flow of wellbore fluids in the annulus. For example, a packer may be formed on the outer surface of a completion string which is run into an outer casing or an uncased hole. The packer is run with the string to a downhole location, and is inflated or expanded into contact with the inner surface of the outer casing or openhole to create a seal in the annulus. To provide an effective seal, fluid must be prevented from passing through the space or micro-annulus between the packer and the completion, as well as between the packer and the outer casing or openhole.
Isolation tools are not exclusively run on completion strings. For example, in some applications they form a seal between a mandrel which forms part of a specialised tool and an outer surface. In other applications they may be run on coiled tubing, wireline and slickline tools.
Conventional packers are actuated by mechanical or hydraulic systems. More recently, packers have been developed which include mantles of swellable elastomeric material formed around tubular bodies. The swellable elastomer is selected to increase in volume on exposure to at least one triggering fluid, which may be a hydrocarbon fluid or an aqueous fluid. The packer may be run to a downhole location in its unexpanded, unswollen state, where it is exposed to a wellbore fluid and caused to swell. The design, dimensions, and swelling characteristics are selected such that the swellable mantle creates a fluid seal in the annulus, thereby isolating one wellbore section from another. Swellable packers have several advantages over conventional packers, including passive actuation, simplicity of construction, and robustness in long term isolation applications. Examples of swellable packers and suitable materials are described in GB 2411918.
It is common for a cable or line to be run parallel to production tubing or another tubular in the well. The cable or line may for example be a conduit for fluids, a hydraulic control line, or may be an electrical or optical conductor which transmits power, data or a control signal. The cable will be secured to the tubing at intervals by clamps, which also provide a protective function. It will often be necessary for a cable or line to pass a packer which creates a seal in the annulus between the tubing and an outer casing. Conventionally, cable or line sections have been integrated into the packer body, with terminal connections provided above and below the packer to allow the path provided by the cable or line to be re-established. However, providing connections for cables or lines in this way has drawbacks. These include poor contact, mechanical weaknesses in the cable or line, and corrosion or leakage paths. Assembly of the packers and connection of the cable or control lines on the rig floor may also be difficult and time-consuming.
FIG. 1 of the drawings shows a swellable packer according to WO 04/057715, generally depicted at 10, formed on a tubular body 12 having a longitudinal axis L. The packer 10 comprises an expanding mantle 15 of cylindrical form located around the body 12. The expanding mantle 15 is formed from a material selected to expand on exposure to at least one predetermined fluid, and is shown here in its swollen condition. The dimensions of the packer 10 and the characteristics of the swellable material of the expanding portion 15 are selected such that the expanding portion forms a seal with a casing 19 in use, which prevents the flow of fluids past the body 12. A cable 22 extends through the packer 10 in an opening 21, and is disposed in the opening through a slit 23.
The arrangement of WO 04/057715 provides a mechanism for passing a cable or a line through a packer, but does suffer from drawbacks. Firstly, the slit is designed to be closed prior to swelling of the apparatus, and must be opened with specialised equipment which holds open a portion of the slit while the cable is disposed into the opening. This equipment requires capital expenditure, operation by trained personnel, and space on the rig floor.
In addition, to allow effective opening of the slit, the material used for the packer must be sufficiently pliable. This places limitations on the materials used, which may mean that preferred swelling materials for some well environments are not available. The slit is designed to be self-closing, but a sufficiently pliable material may not close effectively, which could leave the apparatus liable to hang up or snag on protrusions during run-in. Should the cable hang-up, it could become displaced from the slit.
The slit and opening of WO 04/057715 must be formed using special tooling, and the opening must be formed to a size corresponding to the cable or line for the particular application.
WO 05/090743 discloses a system for sealing an annular space around a control lined for an inflow control device (ICD). A seal layer has an inner surface provided with a recess for receiving a control line, and on an opposing side is provided with a slit which allows the seal layer to be opened for radial application to a tubular/
Although the tool of WO 05/090743 is a convenient way of applying a seal to a tubular, it does have limitations. The control line and its cover is placed against the tubing and extends through the sealed layer. This creates a potential leak path between the cover and the pipe, which will be maintained even after swelling of the seal layer, and which limits the isolation capabilities of the device. In addition, the integrity of the seal relies entirely on radial swelling pressure. The sealing of the layer against the pipe is dependent on sufficient force across the radius of the seal layer between the cylindrical surface of the tubular and the inner surface wellbore.
The application of the seal layer in WO 05/090743 relies on resilient deformation of the seal material. This places limitations on the materials that can be used, which may mean that preferred swelling materials for some well environments are not available. In addition, the application method relies on the resilience created by the longitudinal recess for the control line. This may create some limitations to the types of control line that can be accommodated. For example, a single control line would require a smaller recess, which may not be sufficiently large to allow deformation of the seal member around the tubular. Furthermore, there are limitations on the number of longitudinal recesses that can be provided in the seal layer, as this will affect the overall integrity of the seal and clamping force that can be applied to the device.
The provision of bores for receiving the bolts of course removes volume from the seal material and may create a potential weak point in the seal. The fastening mechanism itself also inhibits the natural swelling profile of the seal member in the vicinity of the bolt, resulting in stress and shear forces being applied to the seal. Over continued use, which may include cyclical swelling, this could introduce failure modes into the seal.
There is generally a need to provide a packer and/or an associated cable or line feedthrough method which may be manufactured and assembled more efficiently than in the case of the prior art, and which is flexible in application to a variety of wellbore scenarios.
It is amongst the aims and objects of the invention to overcome or mitigate the drawbacks and disadvantages of prior art apparatus and methods.
Further aims and objects will become apparent from the following description.
According to a first aspect of the invention there is provided an apparatus for creating a seal in a wellbore, the apparatus comprising:
a swellable portion comprising a material selected to expand on exposure to at least one predetermined fluid, wherein the swellable portion comprises a formation open to a longitudinal surface, the formation configured to provide a pathway for a cable or line to extend through the swellable portion.
The swellable portion may have an expanded condition which provides a seal in a wellbore annulus. The apparatus may comprise a longitudinal body, in which case the swellable portion may provide a seal between the longitudinal body and an outer surface. The outer surface may be the internal surface of a casing or an uncased borehole.
The formation may be configured to receive an insert. The insert may be configured to be disposed between the pathway for a cable or line and an outside surface of the swellable portion. The insert may be configured to create a seal between the pathway for the cable or line and an outer surface. Alternatively or in addition, the insert may be configured to provide a seal with the swellable portion and/or a longitudinal body of the apparatus.
The insert may at least partially enclose the cable or line in use. The insert may be configured to be disposed between the cable or line and an outside surface of the swellable portion. The insert may be configured to create a seal between the cable or line and an outer surface. Alternatively or in addition, the insert may be configured to provide a seal between the cable or line and the swellable portion and/or a longitudinal body of the apparatus.
The insert and the formation may together define the pathway for the cable or line through the swellable portion.
The insert may be configured to be coupled to a cable or line. The insert may be configured coupled to a cable or line such that the cable or line is at least partially enclosed or encapsulated.
The insert may be configured to be coupled to a cable or line prior to being received in the formation. Thus the cable or line and the insert may together be received in the formation.
The insert is preferably provided with a recess for receiving a cable or line. The recess may be dimensioned for an interference fit with a cable or line. The insert may be provided with engaging portions for coupling to a cable or line.
The insert may comprise a substantially rectangular outer profile. The outer profile may be dimensioned to be an interference fit with the formation of the swellable portion. The insert may be elongated, and may be formed to a length substantially equal to the length of the swellable portion.
The insert may comprise a main body and a pair of side walls, and may comprise a substantially u-shaped or c-shaped profile. The u-shaped or c-shaped profile may define a recess for receiving the cable or line.
The insert may be resilient and may retain the cable or line, for example by partially or fully surrounding the cable or line. The insert may comprise a clip-on member that clips around a cable or line, and may be bonded in position through the use of an adhesive or other bonding agent.
Preferably, the insert comprises a material selected to expand on exposure to at least one predetermined fluid. The insert may be formed from a material selected to have substantially the same swelling characteristics as the swellable portion. Alternatively, the insert may be formed from a material selected to differ in one or more of the following characteristics: fluid penetration, fluid absorption, swelling coefficient, swelling rate, elongation coefficient, hardness, resilience, elasticity, and density. It may be desirable for the insert to expand at a different rate to the swellable portion.
The apparatus may further comprise means for securing the insert and/or cable to the swellable portion and/or body, which may comprise a bonding agent. Alternatively, or in addition, the apparatus may comprise a mechanical attachment means for securing the insert and/or cable to the swellable portion and/or body, which is preferably an end ring. The mechanical attachment means may be clamped onto the body, and may comprise a plurality of hinged clamping members. Alternatively, the mechanical attachment means is configured to be slipped onto the body.
The apparatus may comprise an end ring having a recess for receiving the cable or line. The end ring may comprise a removable securing member which retains a cable or line extending through the recess in the end ring. The securing member may be configured to be attached to the end ring over a cable or line extending through the recess.
According to a second aspect of the invention there is provided an assembly for creating a seal in a wellbore, the assembly comprising:    a longitudinal body;    a swellable portion formed on the body, the swellable portion comprising a material selected to expand on exposure to at least one predetermined fluid and having a formation providing a pathway for a cable or line to extend through the swellable portion;    and an insert configured to be received in the formation.
The apparatus of the second aspect of the invention may include one or more features of first aspect or its preferred embodiments.
According to a third aspect of the invention there is provided a method of forming a downhole apparatus, the method comprising the steps of:                (a) Providing a swellable portion on a longitudinal body, the swellable portion comprising a material selected to expand on exposure to at least one predetermined fluid;        (b) Providing an open formation in a longitudinal surface of the swellable portion, the open formation configured to receive a cable or line.        
The method may include the additional step of providing a cable or line in the formation.
The method may include the additional step of providing an insert in the formation.
The method may include the step of coupling an insert to a cable or line and providing the combined insert and cable or line in the formation.
According to a fourth aspect of the invention, there is a provided a method of forming a seal in a downhole environment, the method comprising the steps of:                (a) Providing an apparatus in accordance with the first aspect of the invention or an assembly in accordance with a the second aspect of the invention;        (b) Running the apparatus or assembly to a downhole location;        (c) Exposing the swellable portion to a wellbore fluid to expand the swellable portion and create a seal.        
The apparatus or assembly may comprise an insert, the insert comprising a material selected to expand on exposure to at least one predetermined fluid, and the method may comprise the additional step of exposing the insert to a wellbore fluid to expand the insert.
The method of the third or fourth aspects of the invention may include one or more features of first or second aspects or its preferred embodiments.
According to a fifth aspect of the invention there is provided an apparatus for providing a seal in a wellbore, the apparatus comprising: a longitudinal body; a swellable portion formed on the body, the swellable portion comprising a material selected to expand on exposure to at least one predetermined fluid and having a formation providing a pathway for a cable or line to extend through the swellable portion; wherein the formation is a longitudinal recess open to the outer surface of the swellable portion.
The recess may be open to the outer surface in an unswollen condition of the swellable portion. The recess may accommodate an insert. Embodiments of the fifth aspect of the invention may include preferred and optional features of any of the first to fourth aspects of the invention, and/or features of the appended claims.